a. Field of the Invention
The present invention relates to detection of an optimum working condition for wire electric discharge machining.
b. Description of the Related Art
In wire electric discharge machining, there are five-hundred to six-hundred working conditions such as material and thickness of a workpiece, material and diameter of a wire electrode, jetting pressure of working fluid from a nozzle, and distance between the nozzle and the workpiece, and further, as electric conditions, no-load voltage, condenser capacity in the case of capacitor discharge, charge on-pulse width, charge current, off-time duration, working speed and so on. Thus, it is extremely difficult to set the working conditions one by one. Moreover, conventionally, the setting of these conditions is generally made relying upon experience and perception of an operator. Hence, this method is encumbered with difficulties in setting optimum and most efficient working conditions, and in ascertaining whether or not the working conditions thus set are optimum ones. After all, trial-and-error is required in setting the working conditions.
To eliminate the drawback of the above mentioned working-condition setting by the operator, the following methods are known, for instance. In a first method (refer to Japanese Patent Application Laid-Open No. Sho 59-7523), among various sets of electric working conditions, which are stored beforehand in a control device in a manner corresponding to thicknesses of workpieces, a set of conditions are selected in dependence on the workpiece thickness determined on the basis of working electric current and working speed, to obtain working conditions suitable for the thus determined workpiece thickness. In another method (refer to Japanese Patent Application Laid-Open No. Sho 54-13096), electric working conditions and working speeds, corresponding to thicknesses of workpieces, are stored in a control device, and the electric working conditions are changed in accordance with the working speed. In still another method (refer to Japanese Patent Application Laid-Open No. Sho 49-108696), respective numbers for which good and bad electric discharge occur are counted, and electric working conditions are changed in dependence upon the ratio of these counts.
However, changing the working conditions in dependence upon the workpiece thickness, as disclosed in the above Japanese Patent Application Laid-Open No. Sho 59-7523 and No. Sho 54-13096, has a problem in that the electric working conditions cannot be changed in accordance with changes in factors other than the workpiece thickness such as the jetting pressure of the working fluid from the nozzle and the distance between the nozzle and the workpiece, despite that the electric working conditions should be changed with changes in these factors.
Further, according to the method disclosed in the above Japanese Patent Application Laid-Open No. Sho 49-108696, the working conditions can vary during machining, despite that the working conditions should not be varied, but should be kept unchanged, if the workpiece thickness remains constant, because such variations during wire cut electric discharge machining may result in the workpiece being scratched on its surface. After all, this conventional method has a drawback in that it is unable to carry out efficient wire cut electric discharge machining.